Open Data supplied by Natural Environment Research Council (NERC)

Niskin Bottle

The Niskin bottle is a device used by oceanographers to collect subsurface seawater samples. It is a plastic bottle with caps and rubber seals at each end and is deployed with the caps held open, allowing free-flushing of the bottle as it moves through the water column.

Standard Niskin

The standard version of the bottle includes a plastic-coated metal spring or elastic cord running through the interior of the bottle that joins the two caps, and the caps are held open against the spring by plastic lanyards. When the bottle reaches the desired depth the lanyards are released by a pressure-actuated switch, command signal or messenger weight and the caps are forced shut and sealed, trapping the seawater sample.

Lever Action Niskin

The Lever Action Niskin Bottle differs from the standard version, in that the caps are held open during deployment by externally mounted stainless steel springs rather than an internal spring or cord. Lever Action Niskins are recommended for applications where a completely clear sample chamber is critical or for use in deep cold water.

Clean Sampling

A modified version of the standard Niskin bottle has been developed for clean sampling. This is teflon-coated and uses a latex cord to close the caps rather than a metal spring. The clean version of the Levered Action Niskin bottle is also teflon-coated and uses epoxy covered springs in place of the stainless steel springs. These bottles are specifically designed to minimise metal contamination when sampling trace metals.

Deployment

Bottles may be deployed singly clamped to a wire or in groups of up to 48 on a rosette. Standard bottles have a capacity between 1.7 and 30 L, while Lever Action bottles have a capacity between 1.7 and 12 L. Reversing thermometers may be attached to a spring-loaded disk that rotates through 180° on bottle closure.

Oxygen concentrations from CTD bottle samples collected during AMT17

Originator's Protocol for Data Acquisition and Analysis

These data originate from analyses on samples collected from 12 CTD rosette bottles from all CTD casts. Water samples were taken directly from the bottles in the Sea-Bird CTD rosette system using silicon tubing.

References Cited

Instrumentation Description

Not applicable for this data set.

BODC Data Processing Procedures

Data were submitted via email in an Excel spreadsheet archived under BODC's accession number PML060007. Sample metadata (CTD cast, date, latitude, longitude, bottle number and depth) were checked against information held in the database. There were a number of small discrepancies. There were two CTD055 casts according to this worksheet, one with the steel and one with the titanium rig. The problem resulted from a mistyped CTD cast number, which was noted and corrected with CTD056t originally being referred to as CTD055t. Cast 55 was carried out on the steel rig and the depths and ROSPOS of the CTD055t cast match the CTD056t cast.

When comparing the data with measurements from the oxygen sensors on the CTD packages, it also became obvious that the depths provided in the originator's spreadsheet were suspect for some of the casts. Investigation was able to trace the problem back to a mix-up when attributing real depth to the data based on the Niskin bottle reference number. The depths were clearly assigned assuming the reference number was firing sequence while in fact it was rosette position. While for most casts these were identical, for a few casts this led to major errors in depth assignment. Once the depths were attributed based on rosette position rather than firing sequence the major outliers from the data calibration were no longer outliers. This provided the confidence that this was the correct way to assign the data. Decision was also corroborated against the hand-written bottle firing log sheets.

The temperature of fixation of the oxygen samples was also provided by the originators but not loaded to the database at the time of processing. These supplementary data are available on request.

The concentration data were provided in micromoles per litre. These units for the concentration data were consistent with the BODC parameter code units and no conversion was applied.

The data were reformatted and loaded in BODC's samples database under Oracle Relational Database Management System. Data were marked up with BODC parameter codes and loaded into the database. Individual samples were matched through rosette sampling bottle and depth.

A parameter mapping table is provided below;

Originator's Parameter

Units

Description

BODC Parameter Code

Units

Comments

O2 conc

µmol l -1

Concentration of oxygen {O 2 } per unit volume of the water body [dissolved phase] by Winkler titration

DOXYWITX

µmol l -1

n/a

Data Quality Report

BODC was not advised of any specific quality issues with the data. The data were checked visually and used for the calibration of the CTD sensor. No values were flagged by BODC.

Problem Report

The Atlantic Meridional Transect - Phase 2 (2002-2006)

Who was involved in the project?

The Atlantic Meridional Transect Phase 2 was designed by and implemented by a number of UK research centres and universities. The programme was hosted by Plymouth Marine Laboratory in collaboration with the National Oceanography Centre, Southampton. The universities involved were:

University of Liverpool

University of Newcastle

University of Plymouth

University of Southampton

University of East Anglia

What was the project about?

AMT began in 1995, with scientific aims to assess mesoscale to basin scale phytoplankton processes, the functional interpretation of bio-optical signatures and the seasonal, regional and latitudinal variations in mesozooplankton dynamics. In 2002, when the programme restarted, the scientific aims were broadened to address a suite of cross-disciplinary questions concerning ocean plankton ecology and biogeochemistry and the links to atmospheric processes.

The objectives included the determination of:

how the structure, functional properties and trophic status of the major planktonic ecosystems vary in space and time

how physical processes control the rates of nutrient supply to the planktonic ecosystem

how atmosphere-ocean exchange and photo-degradation influence the formation and fate of organic matter

The data were collected with the aim of being distributed for use in the development of models to describe the interactions between the global climate system and ocean biogeochemistry.

When was the project active?

The second phase of funding allowed the project to continue for the period 2002 to 2006 and consisted of six research cruises. The first phase of the AMT programme ran from 1995 to 2000.

Brief summary of the project fieldwork/data

The fieldwork on the first three cruises was carried out along transects from the UK to the Falkland Islands in September and from the Falkland Islands to the UK in April. The last three cruises followed a cruise track between the UK and South Africa, only deviating from the traditional transect in the southern hemisphere. During this phase the research cruises sampled further into the centre of the North and South Atlantic Ocean and also along the north-west coast of Africa where upwelled nutrient rich water is known to provide a significant source of climatically important gases.

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.